This application claims the benefit of Korean Patent Application No. 1999-31488, filed on Jul. 31, 1999, under 35 U.S.C. xc2xa7 119, the entirety of which is hereby incorporated by reference.
1. Field of the invention
The present invention relates to an alignment key, more particularly to an alignment method and alignment key used for an alignment between two substrates of a liquid crystal display device (LCD).
2. Description of Related Art
A liquid crystal display device (LCD) is comprised of two substrates opposite to and spaced from each other by a predetermined distance, liquid crystal between the two substrates, and a plurality of layers formed between the liquid crystal and the two substrates.
Alignment keys are formed on both of the substrates as a means of alignment of two substrates. An alignment state is checked by whether the alignment keys are correctly aligned with each other or not.
Recently, since the LCD tends to be much more integrated than before for a full-color implementation close to a natural color, distances between the components have been narrowed more and more.
Therefore, since only a little misalignment may cause a bad color characteristic and a low yield, the importance of good alignment has been rising.
Now, an alignment key of the LCD will be described with reference to accompanying drawings
FIG. 1 is a plan view illustrating the alignment key of a LCD formed on a substrate. The substrate 1 has an active region 3 on which the substantial components are arranged and a non-active region 5 that will be removed and disused soon after the alignment process is completed. The non-active region 5 has cross-shaped alignment keys on each edge thereof.
The alignment keys 7 formed on the upper and lower substrates, respectively, become a means of alignment between the upper and lower substrates.
FIG. 2a is a plan view illustrating a conventional alignment key formed on the upper substrate of the LCD. The cross-shaped alignment key 10 includes four align marks 10a, 10b, 10c and 10d, which are spaced from each other by a predetermined distance.
FIG. 2b also shows the cross-shaped alignment key formed on the lower substrate. Though the upper and lower alignment keys 10 and 12 are made in the beginning process, they are used in the alignment process.
When the upper substrate is aligned with the lower substrate, as shown in FIG. 2c, the upper and lower alignment keys 10 and 12 look as if they are formed on the same substrate. When the alignment key 10 of the upper substrate is located within the alignment key 12 of the lower substrate, it is assumed that the upper substrate is correctly aligned with the lower substrate. In general, two alignment keys are formed on two edges of the substrates in a diagonal line direction. In some cases, four alignment keys may be formed on each edge of the substrates.
The alignment key used in the related art LCD, however, is a means for checking a misalignment state between the upper and lower substrates rather than for measuring an alignment error between two substrates.
Though an alignment error between the upper and lower substrates may be checked more or less, it is impossible to measure an alignment error.
Therefore, it is required to find a misalignment direction whether they are misarranged in a row direction or in a column direction.
An object of the present invention is to provide an alignment method and an alignment key of the LCD capable of finding misalignment direction.
Another object of the present invention is to provide an alignment method and an alignment key of the LCD capable of monitoring the process errors immediately.
The invention provides, in one embodiment, a liquid crystal display device, comprising: a first substrate including a first alignment key formed thereon, the first alignment key having at least first and second alignment marks spaced from each other; and a second substrate to be aligned with the first substrate, including a second alignment key formed thereon, the second alignment key having at least third and fourth alignment marks, the third alignment mark being formed at a corresponding position of the first alignment mark of the first alignment key, the fourth alignment mark being formed at a distant position from the second alignment mark of the first alignment key, the distant position being measured in advance.
The alignment marks of the first alignment key are disposed in a matrix form. The alignment marks of the second alignment key are disposed in a matrix form. The number of the alignment marks of the first alignment key is substantially same as that of the second alignment key. A distance from the second alignment mark of the first alignment key to the fourth alignment mark of the second alignment key is indicated by a coordinate. The coordinate is an X-Y coordinate.
Each alignment mark of the first alignment key has a rectangular shape. Each alignment mark of the second alignment key has a rectangular shape of a rectangular. Each alignment mark of the first alignment key has a circular shape.
Each alignment mark of the second alignment key has a shape of a circle.
Each distance between a fifth alignment mark of the first alignment key and a corresponding alignment mark of the second alignment key increases as the fifth alignment mark of the first alignment key becomes more distant from a center of the second alignment key.
The invention provides, in another embodiment, a liquid crystal display device comprising: a first substrate including a first alignment key formed thereon, said first alignment key being a matrix of uniformly distributed alignment marks; and a second substrate including a second alignment key formed thereon, said second alignment key being a matrix of non-uniformly distributed alignment marks. The first alignment key and said second alignment key together define a plurality of pairs of corresponding alignment marks. Alignment of said first alignment key and said second alignment key causes a first subset (e.g., one pair) of said plurality of alignment mark pairs to align correctly while also causing a second subset (e.g., another pair) of said plurality of alignment mark pairs to align incorrectly. Misalignment of said first alignment key and said second alignment key causes said first subset of said plurality of alignment mark pairs to align incorrectly while also causing a third subset (e.g., one pair) of said second subset to align correctly. Locations of said third subset relative to said first subset are indicative of a degree to which said second alignment key is misaligned with said first alignment key.
The foregoing and other objectives of the present invention will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.